The practice of continuously casting molten metal in a continuous caster most commonly employed at present is carried out by the vertical continuous casting process which comprises casting molten metal received from a ladle into a tundish, through a teeming nozzle attached to the bottom wall of the tundish in downward projection, into a mold arranged vertically below the teeming nozzle to form a cast strand, and extracting the cast strand thus formed into a long strand from the lower end of the mold while cooling. The horizontal continuous casting process has recently been put to practical use, which comprises casting molten metal, through a teeming nozzle attached to the lowermost end of the side wall of a tundish horizontally in projection, into a mold arranged horizontally at the tip of the teeming nozzle on the same axis as the horizontal axis of said teeming nozzle, to form a cast strand, and extracting the cast strand thus formed into a long strand always horizontally from the mold while cooling.
In the above-mentioned continuous casting operations, the temperature of the molten metal received in the tundish exerts an important effect on the subsequent casting operations in the aspect of manufacturing a cast strand excellent in quality and free of such troubles as breakout. To continuously measure the temperature of the molten metal received in the tundish is therefore very important when manufacturing efficiency a cast strand.
The usual practice for measuring the temperature of molten metal received in a vessel such as a tundish as mentioned above has comprised connecting a probe having a thermocouple housed in an aluminum protecting tube to lead wires connected to a pyrometer, vertically lowering downward said probe into the vessel to a prescribed position in the vessel, and immersing said probe into the molten metal received in the vessel, thereby measuring the temperature of said molten metal by means of said probe.
In the above-mentioned conventional method for measuring the temperature of molten metal, however, the probe immersed in the molten metal is eroded by molten slag floating on the surface of the molten metal. It has therefore been difficult to immerse said probe for a long period of time and thus to continuously measure the temperature of the molten metal.
In addition, since the level of the molten metal recived in a tundish, for example, varies with the progress of casting, the probe positioned at a prescribed position in the tundish changes its relative position to the level of the molten metal under the effect of variation of the above-mentioned level of molten metal, and in some cases, the probe may measure the temperature of molten slag when the probe is located in the layer of molten slag floating on the surface of the molten metal. The method for measuring the temperature mentioned above tended to easily cause an error in the result of measurement.
Furthermore, since the probe is vertically lowered downward into a vessel such as a tundish, the position of attachment of the thermocouple housed in the probe and connected to the lead wires connecting with the pyrometer is located above the vessel containing the molten metal. As a result, said lead wires tended to be easily burnt out under the effect of radiation heat from the molten metal received in the vessel. In order to prevent the above-mentioned burnout of the lead wires, it is necessary to extend the thermocouple housed in the probe far to the outside of the probe so that the thermocouple may be connected to the lead wires at a position not affected by the radiation heat from the molten metal. The extension of the thermocouple requires, however, a large quantity of expensive thermocouple, thus leading to the problem of high cost.
Under such circumstances, there is a strong demand for the development of a method for measuring the temperature of molten metal received in a vessel, which permits continuous measurement, for a long period of time, of the temperature of the molten metal received in a molten metal vessel, especially in a tundish for continous casting, and also enables to prevent an error in measurement result from occurring irrespective of the variation in the level of the molten metal caused by the progress of casting and to prevent the lead wires attached to the probe from being burnt out. Such a method for measuring the temperature is not however as yet proposed.